Without such differences, it would be difficult to target and kill bacterial cells once they get into the human body.

The difference between a bacterial cell and human cell help us fight bacterial infections. Antibiotics when administered, into the human body act in such a way that only bacterial cells are killed while sparing humans.

Some of the common targets to achieve this safe drug action are the cell wall, 70s ribosomes, DNA gyrases, etc.

Ex: Penicillins kills bacteria by acting on their cell wall. Since human cell lacks a cell wall, human cells are not affected by it. Similarly, streptomycin acts only on 70s ribosomes and prevent their protein synthesis while in human cells there are 80s ribosomes. So they are not affected by the antibiotics.